Restarting a Cut After Losing Arc

If you lose arc in the middle of a long cut, you don’t need to scrap the part or start over. CommandCNC provides a way to restart from where the cut stopped using the Disable Torch feature. This allows you to resume motion and re-ignite the torch at the correct point in the program.

Why This Works

When you restart a program from the middle:

The machine can move along the programmed toolpath without firing the torch.
Once it reaches the point where the arc was lost, you can re-enable the torch manually.
This prevents double-cutting earlier sections and lets you salvage the part.

Step-by-Step Procedure

Step 1 – Prepare the Torch

In CommandCNC, locate the Torch control section.
Check the box labeled Disable Torch.
- ✅ When checked, the machine will run the program without firing the torch.

Step 2 – Select a Restart Point

Open the G-code program view.
Scroll to the section where the cut was interrupted.
Look for the last M5 command (this is the G-code that turns the torch off) just before the cut you want to restart.
- ⚠️ Do not pick an M3 (torch on) line, as that may cause misalignment.
Highlight or click on that line.

Step 3 – Run From Line

Click the Run From Line button.
The machine will begin moving along the toolpath starting from the selected point.
Because Disable Torch is still active, the torch will not fire yet — it will only motion along the path.

Step 4 – Re-Enable Torch at the Right Spot

Keep your mouse pointer ready over the Disable Torch checkbox.
As the machine approaches the exact point where the arc was lost:
- Uncheck Disable Torch.
- The torch will fire immediately.
The cut will continue from where it left off.

Troubleshooting Arc Loss

If you often lose arc during long cuts, investigate these common causes:

1. Consumables

Worn electrode or nozzle can cause unstable arc.
Inspect and replace regularly, especially if cut quality is declining.

2. Poor Work Clamp Connection

Ensure the ground clamp is clean, tight, and attached directly to the material.
Rust, paint, or mill scale under the clamp can break arc continuity.

3. Water or Slag Interference

Water splashing onto the plate can short the arc.
Accumulated dross may also interfere with the cut path.

4. Incorrect Torch Height Control (THC) Settings

Torch diving too low may extinguish the arc.
Verify Z height, pierce delay, and voltage settings.

5. Gas and Air Supply

Low or inconsistent air pressure will cause arc failure.
Check compressor, filters, and regulators.

6. Loose Connections or Noise Issues

Inspect all torch leads and cables for wear or loose fittings.
Electrical noise (ground loops, RS485 hub problems) can cause false arc loss.

Best Practices

Always keep spare consumables on hand.
Perform a quick check of ground, air supply, and THC settings before long jobs.
Test the restart method on scrap material to build operator confidence.

✅ With this procedure, you can salvage interrupted jobs and reduce future arc loss by fixing root causes.

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